This invention relates generally to providing precisely measured amounts of granular materials and, optionally, precisely measured amounts of coloring agent(s), particularly pigment in liquid form, preparatory to further processing of the combined granular materials and, optionally, liquid coloring agent(s), and specifically to weigh scale blenders, optionally in combination with color addition pumps, providing precisely measured amounts of plastic resin material, and, optionally liquid coloring agents, and mixing these components prior to supplying the blended mixture to plastics manufacturing and processing equipment such as plastic injection molding, compression molding and extrusion equipment.
The modern weigh scale blender was essentially originated by the applicant and is widely used throughout the world by industries concerned with precision feeding of granular material, especially plastic resin material.
Weigh scale blenders operate by blending solid plastic resin material components and additives, by weight, in batches. Typically batches of material may consist of several solid material components. One of these may be xe2x80x9cregrindxe2x80x9d, consisting of ground plastic resin which had previously been molded or extruded and which either resulted in a defective product or was excess material not formed into a desired product.
Another component may be xe2x80x9cnaturalxe2x80x9d plastic resin which is virgin in nature in the sense that it has not previously been processed into a molded or extruded plastic part.
Yet another component may be a solid color material, typically flakes or freeze dried material, used to produce a desired color of the finished plastic part.
Still yet another component may be an additive used to adjust the blend to provide required performance characteristics during molding, extrusion or subsequent processing.
The weigh scale blender typically includes hoppers for each of the components of the solid material to be blended together. Typically several hoppers or several compartments in a hopper may be provided, such as one compartment for xe2x80x9cregrindxe2x80x9d material, one compartment for xe2x80x9cnaturalxe2x80x9d material, one component for solid color additive material and one compartment for xe2x80x9cadditivexe2x80x9d.
When the weigh scale blender operates, the unit desirably operates automatically, adding each of the component solid materials in the proper, desired percentages. Each solid material component is dispensed by weight into a single weigh bin. Once the proper amounts of each component have been serially dispensed into the weigh bin, all of the components are dropped together into a mixing chamber from the weigh bin.
Mixing is performed, preferably continuously, and preferably even as additional batches component are dispensed in the mixing chamber. When mixing is complete, the resulting blend is preferably provided directly to the desired molding or extrusion machine.
It is known to provide feedback control of the dispensed amounts of each solid material component provided to the weigh bin and measured by weight so that in the event of an error in the amount of a dispensed component, the succeeding batch may have the blend adjusted to account for the error detected in the preceding batch of blended material.
As one of the components forming a part of the resulting blend it is known to supply solid color additives to the blend in order to provide a blend of a desired color. These color additives may be flaked pigments on wax carriers or in freeze dried form. It is also known to provide the color as pigment powder constituting one component of the resulting blend.
When preparing blends of resinous plastic material for molding or extrusion, when color amounts are too low the error is visible and a correction to increase color may be effectuated by an operator. However, when color amounts are too high, the problem is not visible and operators manually operating the process normally do not make any adjustment in the amount of color. Hence adjustments are frequently made to increase the amount of color materials supplied to a blend but almost never is the amount of color supplied to the blend reduced.
Liquid color material cannot be preblended into one of the solid material components and stored because of the danger inherent and difficulties attendant to clean-up in the event of component failure. Hence, liquid color, when used in plastics material processing heretofore, has been metered directly into the throat of a molding press or an extrusion machine, at a position to join the solid resinous material blend just prior to the molding or extrusion operation. This approach creates difficulties, among them being compensating for addition of pre-colored regrind solid material to the material mix.
When regrind is added to the blend of plastic resin materials, the regrind already contains the necessary color; such regrind need not be colored a second time. When metering resinous material at the throat of a molding press or an extrusion machine, such metering is conventionally performed volumetrically. Hence, the presence of already colored regrind, not requiring additional coloration, cannot be detected. As a result, excess liquid color is typically added to the blend, sometimes producing an unacceptable product and always resulting in the use of unneeded color material, which is undesirable and results in unnecessary expense.
Weigh scale blenders typically use one or more load cells to detect the weight of the weigh bin and material contained therein. Vibrational and shock loading of the load cells may result in erroneous measurements of the weight of the weigh bin and the material contained therein. These erroneous measurements may result in addition of excess material or an insufficient amount of a material component in a subsequent batch thereby producing a batch of blended material deviating from the desired specifications. The load cells are subject to some vibration and shock loading due to the presence of pneumatic piston-cylinder combinations typically connected to the frame of the weigh scale blender and used to dispense solid granular resinous material from a hopper downwardly into the load bin.
Further vibrational and shock loading of the load cells may result from use of typically pneumatically driven piston-cylinder combinations to empty the weigh bin when the weight measurement is complete. Yet further vibrational and shock loading of the load cells may result from operation of the mixing chamber and the motor driving a mixing means within the mixing chamber.
Because the frame of the weigh scale blender must be a rigid, high strength structure to provide the required strength to support the material storage hoppers and other components of the weigh scale blender, the weigh scale blender frame is typically steel. Since the frame is steel and rigid, shock and vibrational loads applied to the frame are readily transmitted along the frame and received by the various components of the weigh scale blender connected to the weigh scale blender frame.
When the weigh scale blender is mounted directly on a plastics material processing machine such as an extruder or, more particularly, an injection molding machine, the load cells of the weigh scale blender can be subjected to very substantial shock and vibrational loading. Injection molding machines have heavy steel platens and molds which open and close as parts are molded and ejected. There is a considerable amount of movement in an injection molding machine and the parts which move are heavy. Hence shock loads, which continuously propagate throughout injection molding machines and hence propagate through the weigh scale blender when the blender frame is bolted to the injection molding machine, maybe quite substantial.
In weigh scale blenders utilizing single load cells, loads on a cell may be substantial. In single load cell weigh scale blenders the single load cell has the weight of the weigh bin cantilevered on an arm and the cell bears the entire weight of the weigh bin and the material contained therein. Hence vibrational loading of the frame of the weigh scale blender may produce substantial vibrational loading of the load cell with stress to the load cell due to the weight carried by the load cell. The cantilevering of the weigh bin from the load cell results in high moments of inertia being applied to the load cell when the load cell is subject to vibration and shock loading.
In one of its aspects this invention provides a weigh scale blender/color addition pump combination where the weigh scale blender includes a frame, a hopper supported on the frame, a weigh bin below the hopper and load sensing means mounted on the frame for sensing weight of the bin including material contained within the bin.
The weigh scale blender further preferably includes preferably pneumatic piston-actuated means, preferably connected with the hopper, for releasing material within the hopper towards the weigh bin. A mix chamber preferably below the bin preferably includes mixing means therewithin.
The weigh scale blender preferably further includes pneumatically actuated means for releasing material within the bin into the mix chamber. A motor preferably rotates the mixing means.
Respecting the combination of the weigh scale blender and the color addition pump means for supplying liquid color to the material mix for blending therewith, the pump means supplying liquid color may desirably be a peristaltic pump or a progressive cavity pump. The liquid color is supplied by such a liquid pump in an amount measured by weight in the blender, in the same manner as the other, solid material components of the resulting material blend are added. Peristaltic pumps are preferred.
Gravimetric blending using a weigh scale blender of the type to which this invention relates permits detection of the presence of colored solid regrind material and resultant adjustment of the amount of liquid color being added. This invention, in one of its aspects combining a liquid color supply pump with a weigh scale blender resulting in addition of liquid color to the material blend provides many of the same advantages as when blending just dry plastic powder and concentrated plastic resin pellets.
When these granular solid and liquid materials are added to the weigh scale blender there is precise metering, no over-coloring and no danger of recoloring regrind material. Hence liquid color material may be added and metered using the same techniques as solid plastic resin material, which techniques are considerably easier, more efficient and more accurate than liquid color handling techniques.
In another of its aspects this invention embraces preparing plastic resin material for manufacturing processing such as molding or extrusion. This includes preferably serially metering respective solid resinous materials to the weigh station until pre-selected weights of the respective materials are at the weigh station. This further includes metering liquid color to the weigh station to join at least one of the materials which have been metered to the station until a pre-selected weight of liquid color is at the weigh station. This further includes providing the serially metered solid materials and the pre-selected weight of liquid color material unitarily to a mixing station. This further embraces mixing the unitarily supplied preferably serially metered solid granular materials and a pre-selected weight of liquid color into a blend preparatory to manufacturing processing via molding or extrusion.
The monitoring is preferably performed continuously and digitally.
The metering of liquid color is preferably performed peristaltically.
In another of its aspects the invention may provide spring-loaded solenoid valve means for actuating the means for releasing material within the hopper, preferably by applying pneumatic pressure to a piston associated with the hopper material releasing means.
The weigh scale blender may further include means for enclosing the solenoid valve means thereby preventing finger actuation of the solenoid valve means. The weigh scale blender may yet further include manually controlled means, adapted for passage through the enclosure means, for overriding the solenoid valve means to result in application of pneumatic pressure to the piston of the hopper material releasing means thereby releasing any material within the hopper and permitting gravity induced flow thereof.
The spring-loaded solenoid valve means for actuating the means for releasing material within the hopper by applying pneumatic pressure to a piston of the hopper material releasing means may include a pressurized air manifold, conduits pneumatically communicating with respective sides of the piston and valve means including a movable stem defining a portion of the valve exterior, for selectably connecting the conduits to the manifold, thereby to move the piston in a selected direction and hence the associated material releasing means between open and closed positions.
There may further be provided a spring for biasing the stem of the valve means towards the position at which the material releasing means is closed. The means enclosing the solenoid valve means for preventing finger actuation thereof may comprise a block, preferably having an internal bore therewithin. The bore is preferably aligned with the stem of the valve. An external surface of the block preferably includes an aperture defining an end of the bore which is sufficiently proximate to the valve means to preclude digital or finger actuation of the valve by contact with the valve stem.
In another of its aspects, the weigh scale blender may include axially self-aligning means for coupling the motor to the mixing means.
Respecting the axially self-aligning means for coupling the motor to the mixing means, the self-aligning coupling means may preferably further include a cylindrical female member having an axially facing central bore formed therein. In such case, the annular female member further preferably includes a pair of retractable pins preferably extending from the end of the member and being adapted for mating connection with the male member.
The male member is preferably cylindrical and preferably has an annular plug extending axially therefrom. The plug preferably includes an axially tapered tip adapted for preferably complemental engagement with the preferably axially tapered wall of the female member bore. The plug further preferably includes a cylindrical wall intermediate the tip portion and the male member.
The male member preferably further includes bores formed therewithin for receipt of the retractable pins when the plug is within the female member bore and the axially tapered annular and cylindrical walls of the male and female members are in preferably respective complementally contacting engagement.
In another of aspects this invention provides a weigh scale blender having a frame, a weigh bin, means connected to the frame for sensing weight of the bin and any material contained therein, a mix chamber below the bin and connected to the frame with mixing means within the mix chamber, means for selectably releasing material in the weigh bin downwardly into the mix chamber with means connecting the weight sensing means to the frame and damping transfer of vibration and shock motion therebetween. The connecting means damping transfer of vibration and shock motion between the frame and the sensing means is elastomeric and is most preferably rubber.
In a yet further aspect of the invention the connecting means which damps transfer of vibration and shock motion between the weight sensing means and the frame includes an elastomeric member interposed between the frame and the weight sensing means. This elastomeric member is preferably annularly disposed about a shaft mutually received by the frame and the mounting portion of the weight sensing means.